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    <title>SNAP Data Processors - The Rayleigh Correction Processor - Algorithm Specification</title>
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        <td class="header">SNAP Data Processors - The Rayleigh Correction Processor - Algorithm Specification</td>
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<h3>Summary</h3>

<p>
    The <em>Rayleigh Correction</em> processing is organised in several steps. First the Rayleigh
    reflectance is computed for every 4x4 pixels window. Then, Rayleigh transmittance and Rayleigh
    spherical albedo are computed for every 4x4 pixels window. Then, the TOA apparent reflectance
    corrected for gaseous absorption &#961;<sub>ng</sub> is corrected for Rayleigh contributions for each pixel in order
    to
    derive the top of aerosol reflectance r<sub>top</sub>. The 4x4 pixels windows do not overlap.
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<p>
    The <em>Rayleigh Correction</em> algorithm has originally been designed for MERIS, but is basically not
    sensor-dependent. The current SNAP processor version also supports OLCI and Sentinel-2 MSI instruments.
    Support for further instruments is planned for future SNAP versions.
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    <img src="images/ray_corr_flow_small.png" alt="Rayleigh Correction Processing Flow"/>

<div style="text-align: center;"><it>The Rayleigh Correction Processing Flow (taken from [1]).</it></div>
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<h3>Algorithms</h3>

<p>
    The underlying algorithms are presented in detail in the MERIS Level 2 Detailed Processing Model [1].
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<h3>References</h3>

<p class="i1">
    <b>[1]</b>
    Bourg, L. (2009): MERIS Level 2 Detailed Processing Model. ACRI-ST, Document No. PO-TN-MEL-GS-0006, 15 July 2009.
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